Wipers driven by mechanical mechanisms cover a normal wipe pattern the limits of which are determined by the parameters of the mechanism. Typically, the mechanism is a four bar linkage. It is often desired to lower the inwipe limit of the wipe pattern, allowing the wiper to be stopped or "parked" at a more unobtrusive position. Myriad park mechanisms exist, most of which reverse the main drive motor at the end of the wipe cycle to cause a link in the system to lengthen. More rare are systems that provide for actively changing the limits of the wipe pattern as the wiper operates. These incorporate a dedicated motor or other power source separate from the main wiper drive motor.
Less common are wipers driven by spatial mechanisms, in which continuous rotation about an axis is translated into oscillation of a wiper post about an arbitrarily chosen axis. Conventional park mechanisms used with four bar linkages would not translate well to a spatial mechanisms. A park mechanism suited to a spatial mechanism, especially one that allowed the wipe pattern to be actively changed, would be useful.